Direct Ceramic Machining (DCM)

Contact: Frank Filser, Peter Kocher

Rapid Prototyping of Ceramic Materials: All-Ceramic Dental Restorations From Laboratory to Market

Artificial dental restorations date back more than 2'500 years. Even before 200 BC, teeth of ivory fixed with gold filaments improved the quality of live for rich and important people [1] (Figure 1). Since the 18th century, porcelain was used in prosthetic dentistry. Due to their low fracture strength and low toughness, these products showed high failure rates. Hence, in 1962 dental bridges strengthened by a metallic substructure that were glazed with porcelain for esthetics were invented [2]. Until recently, these restorations were the standard of excellence. However, despite their durability, these metal-porcelain restorations showed still shortcomings concerning their esthetic appearance, their biocompatibility and corrosion potential as well as a potential of taste distortions and hypersensitivity reactions.

Figure 1. Dental restorations from 2200 years. Left: Etruscian Bridge consisting of a cow teeth fixed with rivets to gold band [1]. Middle: Bridge with a metallic support structure for load bearing and a porcelain glaze for esthetic reasons (photo courtesy of University of Zurich). Right: All-Ceramic bridge with a zirconia support structure and a porcelain glaze (photo courtesy of University of Zurich).

The desire for metal-free or all-ceramic bridges led to a first effort at two groups of researchers at the Chair of Nonmetallic, Inorganic Materials at ETH Zurich and at the University Zurich. They started in the early 1990'ties a first collaboration with the aim to substitute metal-porcelain bridges by an "all-ceramic-teeth-bridge system" and to test the new restorations in clinical trials.

CERCON® - Smart Ceramics

In 1995 the first "all ceramic teeth bridge" was invented at ETH Zurich based on a process that enabled the direct machining of ceramic teeth and bridges. Since then the process and the materials were tested and introduced in the market as CERCON® - Smart Ceramics. The new system consists of materials, processes, and a new computer aided manufacturing machine (CAM) (see Fig. 2, and [2, 3, 4]).

The approach is to machine a pre-fabricated ceramic blank made of zirconia ceramics with a nano-crystalline porous structure in the pre-sintered state (see Fig. 2). After machining the soft ceramic component in the pre-sintered state, it is sintered and thereby shrinks to its? final dimensions. This shrinkage is designed to take place very homogeneously in all spatial directions. The new machine fabricates the complex shape of dentures from the ceramic blanks with high accuracy in an easy, fast, and fully automated way. The machined component obtains its high hardness, high strength, and toughness after the machining step during the final sintering. The veneering of the high strength ceramic framework then adds the required aesthetic and wear characteristics.

This system was developed and tested for the fabrication of all-ceramic dental bridges and crowns. Its clinical indication [5] was proven in controlled studies at the University of Zurich, Clinic for Fixed and Removable Prosthodontics. It showed the superiority characteristics of the new material in respect of highest esthetics demands, excellent biocompatibility and absence of hypersensitivity reactions offering higher quality of live.

CERCON® - Smart Ceramics: From Research to Market

The dental supplier Degussa-Dental introduced this invention in the market in 2001 as the new CERCON® - Smart Ceramics system [6] opening up a new era of ceramics in dentistry.

Rapid Prototyping

Many new mechanical or electronic ceramic components are developed using functional prototypes for testing and evaluation purposes. Especially the fabrication of prototypes made of ceramic materials requires specialized shop-floor equipment, and therefore in case of ceramic components it is often outsourced to external specialized suppliers. Unfortunately long delivery times for these parts slow down the speed of product development and hence raise their time-to-market.
Technical ceramic parts from 5 to 65 mm in size possessing features of 1/10th mm to millimeter were fabricated successfully using the CERCON® approach and thus demonstrate its rapid production capability for ceramic prototypes [7] (see Fig. 3).
Rapid Production of ceramic prototypes offers another field of opportunity for the described approach.

Authors

Frank Filser, Peter Kocher, Ludwig J. Gauckler (Nonmetallic Inorganic Materials, Department of Materials, ETHZ)

Heinz Lüthy, Peter Schärer (Clinic for Fixed and Removable Prosthodontics, Center for Dental and Oral Medicine and Cranio-Maxillofacial Surgery, University of Zurich, CH-8028 Zurich, Switzerland)

References

1. Malvine E. Ring, "Geschichte der Zahnmedizin", Könemann Verlagsgesellschaft, Köln, Germany (1997), (engl. Dentistry, Malvine E. Ring, Harry N. Abrams Inc., New York (1985)).
2. F. Filser, "Direct Ceramic Machining of Ceramic Dental Bridges", PhD Thesis No. 14089, ETH- Zürich (2001)
3. F. Filser, H. Lüthy, P. Schärer, L. Gauckler, "All-Ceramic Dental Bridges by Direct Ceramic Machining (DCM)", in: Materials in Medicine, Materials Day, Department of Materials, Ed. M.O. Speidel, P.J. Uggowitzer, vdf Hochschulverlag AG, ETH Zürich, Zurich, 165-189 (1998).
4. F. Filser, P. Kocher, F. Weibel, H. Lüthy, P. Schärer, L.J. Gauckler, "Reliability and Strength of All-Ceramic Dental Restorations Fabricated by Direct Ceramic Machining (DCM)", International Journal Computerized Dentistry, (4): 89-106 (2001).
5. B. Sturzenegger, A. Fehér, H. Lüthy, M. Schumacher, O. Loeffel, F. Filser, P. Kocher, L.J. Gauckler, P. Schärer, "Klinische Studie von Zirkonoxidbrücken im Seitenzahngebiet hergestellt mit dem DCM-System", Acta Med Dent Helv (5): 131-139 (2000).
6. http://www.cercon-smart-ceramics.com (english) , http://www.cercon-smart-ceramics.de (german)
7. Rapid Manufacturing of High-Tech Ceramics. A Case Study for Dental Application, L.J. Gauckler, P. Kocher and F. Filser, in: Proceedings of the Second International Conference on Shaping of Ceramics, Eds. Jan Luyten and Jean-Pierre Erauw, Mol, Belgium, ISBN 90-5857-005-5, (2002), 259-264.
8. Marketing Rollout of the Cercon - Smart Ceramic System

Please also consult the success stories of the Department.

For further information, consult the papers from Filser, Kocher and Fehér in our literature database or our Cercon pages .